Project Summary/Abstract Cystic fibrosis (CF) is a life limiting monogenetic disease caused by mutations in the cystic fibrosis conductance regulator (CFTR) gene. The lung disease begins in early childhood and with time, airways become permanently colonized by bacteria, inflammation becomes prominent, obstruction worsens, and ~95% of patients die of respiratory failure. While significant advances have been made with small molecule modulator therapies to restore function for some CFTR mutation classes, ~10% of people with CF have not benefited from these strategies. The goal of these proposed studies is to apply the recent advancements in base editing technology to correct CFTR mutations in somatic cells, with a focus on mutation classes that do not respond to small molecule modulator therapies. We will investigate a new class of adenine base editors (ABE) that converts A?T to G?C base pairs. Currently, there are 346 well characterized disease-causing variants of CFTR, and of these, 66% are point mutations. Of all single nucleotide mutations, 46% are potentially correctable using ABE. In this proposal, we will use ABE to modify the following 4 CFTR mutations: 1) R553X and 2) W1282X are the 2nd and 3rd most common premature stop codon mutations. 3) 3849+10kb C>T is a splicing mutation and represents ~12% of CFTR mutations. 4) G551D, the 3rd most common disease-causing mutation, results in defective protein gating and is responsive to Ivacaftor treatment. Here we propose to: 1) show that base editors will correct CFTR in CF cells and correct the anion transporter defect in vitro, 2) define the cell type preferences of editing and the role of cell division in airway cells, and 3) correct the anion channel defect in primary airway epithelia, as well as, critical disease phenotypes in the airways of a pig CF model. Projects 1, 2, and 3 (along with the valuable cores) work closely together to directly address the Program?s goal of developing molecular therapies for CF. The Program effectively focuses a team of talented laboratories to address a shared goal in a highly collaborative environment. Our track record supports our commitment to improving the lives of people with CF and increasing our understanding of lung biology. Our goal is to provide a life-long gene repair strategy that could be adapted to for many CF causing mutations. This proposed research is highly innovative. The reagents, methods, and data generated by these experiments will provide guidance for base editing for other monogenic disorders, thereby significantly advancing the gene therapy field.